Recent studies have demonstrated that Natural killer (NK) cells and possibly other innate cells can remember prior encounters with pathogens. The central focus of the project is to further our knowledge of how activating NK receptors (NKR) can drive the expansion, differentiation, and generation of immunological memory. The concept that NK cells can acquire immunological memory and mediate enhanced responses upon re- encountering pathogens provides a new paradigm that might be exploited in the therapeutic treatment of infectious diseases and cancer. The objective of aim 1 is to determine whether immunological memory in T cells can be generated and maintained by the same activating NKR that we have demonstrated are capable of inducing memory in NK cells. T cells frequently acquire expression of NKR during their differentiation, and the proposed studies will allow us to directly compare the immunological memory driven by a NKR versus the TcR in the same T cell. Further, it will allow us to directly compare memory driven by the same activating NKR in T cells versus NK cells in the same host. In aim 2, we have developed a new tamoxifen-induced NK cell specific reporter mouse model to follow the fate of memory NK cells in situ following immune challenges with pathogens or tumors. This has never been possible previously, without the use of adoptive NK cell transfer procedures. Aim 3 also addresses an important aspect of immunological memory, focusing of the contribution of a well-characterized activating NKR, the CD16 Fc receptor. We will investigate if signals through CD16 can drive or augment the generation of immunological memory in NK cells. This is important because of its implications in the immunotherapeutic use of antibodies in cancer patients that eliminate tumors by antibody- dependent cellular cytotoxicity. Collectively, all aims address the central question of immunological memory driven by activating NKR. Upon successful completion of the proposed studies, we will have new insights into the role of activating NKR on the TcR-dependent adaptive responses and TcR-independent innate responses of memory T cells, will provide the scientific community with a new NK cell reporter mouse that can be used to track the fate of memory NK cells after immunological challenges and inducibly ablate genes in mature NK cells, and determine whether the activating CD16 Fc receptor on NK cells is capable of inducing immunological memory and generating more potent NK cells that provide superior ADCC function in infectious diseases and cancer. Overall, these studies will advance our knowledge of an expanding paradigm of immunological memory driven by innate immune receptors.